1. Field of the Invention
The present invention relates to monitoring devices. The invention more specifically relates to monitoring devices comprising a reader and a data carrier, adapted for wireless data and power transmission. The invention also relates to a method for operating a monitoring device.
In the context of the present disclosure a monitoring device should be understood as a small device designed to be worn by a human user for continuous surveillance of a specific medical condition in the user. The monitoring device consists of a reader and a data carrier.
The reader is powered by an internal primary energy source, such as a battery. The data carrier does not have its own primary source of energy. Therefore the data carrier relies on a wireless inductive power transmission from the reader. A transmitter coil in the reader and a receiver coil in the data carrier together form a system of magnetically coupled inductors. The basic principle relies on generating an alternating current in the transmitter coil. The current in the transmitter coil generates a magnetic field which induces a current in the receiver coil. The current in the receiver coil is used to power the data carrier.
The data carrier has monitoring means, such as electrodes for measuring EEG signals in the human user of the monitoring device. The data collected by the monitoring means are preprocessed by data processing means and wirelessly transmitted to the reader for further processing. The reader receives data from the data carrier through load modulation of the data carrier. In a typical application the further processing in the reader includes determining if a specific medical condition has occurred in the user and alerting the user of this condition. Hereby the size and power consumption of the data carrier can be kept small because the battery and the main part of the signal processing is placed in the reader. This is advantageous in that it makes the data carrier feasible for implantation in the human user. It is especially advantageous to have the data carrier subcutaneously implanted with respect to measurement of EEG signals.
2. The Prior Art
U.S. Pat. No. 5,260,701 discloses a device for the bi-directional transmission of data between a master system and a slave system that uses a single transmission antenna and a single reception antenna, wherein the slave system comprises a switching circuit connected in series between a rectifier circuit and a power supply circuit to modulate the real part of the impedance of the slave system between a high value and a low value when the switching circuit is driven in its opened and closed position by a control signal representative of the data to be transmitted to the master system.
U.S. Pat. No. 6,301,138 discloses a data carrier with load modulation means and with improved power supply in the process of load modulation. Additional means secure that the supply voltage for the data processing means during load modulation can be kept at least at the level of the load modulation during the load modulation pauses. The disclosed additional means includes a voltage multiplier circuit and a charge pump.
It is a feature of the present invention to provide a monitoring device incorporating a reader and a data carrier with improved means for data transmission and energy efficiency, hereby providing a monitoring device with a reduced power consumption.
It is another feature of the present invention to provide an improved method for operating a monitoring device.